Japanese Patent Application Publication No. H08-289542 issued Nov. 1, 1996 discloses an RCC type switching power supply capable of narrowing a wide oscillation frequency range brought about in response to load variation. This power supply is provided with a detection circuit and a control circuit in addition to a switching device, a transformer, etc. constituting the RCC. The detection circuit detects output voltage of the RCC. The control circuit determines ON times of the switching device so as to stabilize output voltage of the RCC based on a signal from the detection circuit. The control circuit also lengthens a minimum OFF time of the switching device as output voltage of the RCC is higher. That is, the control circuit includes an ON time setting circuit and an OFF time setting circuit.
In this power supply, ON and OFF times of the switching device can be also adjusted by changing a signal obtained from the output of the RCC in case load impedance is constant, but the ON time setting circuit and the OFF time setting circuit are required.